Created this sander for use on my 3D printing object. It is a 20mm width and 100mm in length. It consist of 2 parts, the top handle and the bottom base. Both are secure by circular pressure.. no screw is needed.

Use any sandpaper and cut to the length of 230mm x 20mm. Place the sandpaper around the bottom base to the two circular notch. Then place one side of the Top handle slide in together with the sandpaper. Force fit the other end to the notch. It will sit nicely as per the picture.